Structure of the terminal portion of a cable

ABSTRACT

A conductor portion of the terminal portion of a cable is encased in a terminal box having an inlet and outlet provided for accommodating the circulation through the terminal box of a liquid nitrogen coolant. The conductor portion is connected to a conductor leading wire which extends through a bushing up to a normal temperature area. The terminal box and part of the bushing are housed within a tank and the tank has an inlet and outlet provided for accommodating the circulation through the tank of a liquid coolant. The bushing has an inlet and outlet provided for accommodating circulation through the bushing of liquid nitrogen coolant. With the structure so arranged the conductor of the cable is led out up to a normal temperature area with a temperature gradient formed along the conductor leading wire.

[ 1 STRUCTURE OF THE TERMINAL PORTION OF A CABLE [75] Inventors: Isao Kubo, Tokyo; Nobuo Shiseki,

lchikawa, both of Japan [73] Assignee: The Fujikura Cable Works, Limited,

Tokyo, .Iapan [22] Filed: Jan. 30, 1973 [21] Appl. No.: 327,949

[30] Foreign Application Priority Data Feb. 2, '1972 Japan 47-12035 May 25, 1972 Japan 47-52060 [52] U.S. CI..... 174/15 BH, 174/D1G. 6, 174/16 BH [51] Int. Cl. l-l0lb 7/34, H02g 15/22 [58] Field of Search 174/DIG. 6, 15 R, 16 BH, 174/16R,15B1-l,15C,9

[56] References Cited UNITED STATES PATENTS 3,522,361 7/1970 Kafka 174/15 C 3,695,057 10/1972 Moisson-Frankhauser... 174/15 R X 2,704,431 3/1955 Steele l74/DIG. 6

FIBER REINFORCED PLASTIC NITROGEN IMPREGNATED REINFORCED INSULATION VACUUM HEAT 5 INSULATION Apr. 2, 1974 Primary Examiner-Bernard A. Gilheany Assistant Examiner-A. T. Grimley Attorney-Agent. or FirmChittick, Thompson &

Pfund [57] ABSTRACT A conductor portion of the terminal portion of a cable bushing has an inlet and outlet provided for accommodating circulation through the bushing of liquid nitrogen coolant. With the structure so arranged the conductor of the cable is led out up to a normal temperature area with a temperature gradient formed along the conductor leading wire.

4'Claims, 3 Drawing Figures INSULATING OIL FIBER REINFORCED I6 PLASTIC 23 STAINLESS STEEL 24 VACUUM HEAT INSULATION REINFORCED INSULATION uoum 5 1 NITROGEN PATENIEDAPR 2 I974 3301.723

SHEET 1 0F 3 INSULATING l 30 29 L 28 I8 /FIBER REINFORcED GASEOUS 22 I6 PLASTIC NITROGEN i 15 I3 I STAINLESS 27 STEEL 24\VACUUM HEAT FIBER INSULATION REINFORCED\ PLASTIC v REINFORCED i9 INSULATION LIQUID NITROGEN 25 8 z FIBER )i /RE|NFORCED PLASTIC NITROGEN IMPREGNATED REINFORCED INSULATION LIQUID 5 '=I NITROGEN IO U II I I I 2 VACUUM HEAT 5 INSULATION PAIENIEDIPR 2mm 3.801.723

SHEEI 3 [IF 3 GASEOUS NITROGEN 9 INSULATING OIL LIQUID 49% '46 NITROGEN LIQUID HELIUM \L LIQUID HEL|uM 0- I 2. IO H 4 5\L|QU|D 3 NITROGEN PATENTEDAPR 2 I974 SHEET 3 OF 3 uoum NITROGEN 2 m 1x I 1 7172771-- A N r 1! M m mn a l M u m.- rlm W lllllillllllll|lll| N m L M m U L 6 n u R R S I m u E E N O 5 n u n T L l "v. .4 A

ma o o m u 5 6 C FIG. 3

STRUCTURE OF THE TERMINAL PORTION OF A CABLE This invention relates to a structure of the terminal portion of a cableiconductor excellent in heat insulating and electrical characteristics, in which the terminal portion of the conductor is led out up to a normal temperature area through a conductor leading wire.

The terminal portion of a conventional superconductive cable or very low temperature cable is so constructed that the terminal portion of a conductor is led out up to a normal temperature area through a conductor leading wire connected to the conductor. The heat radiation of the conductor or the conductor leading wire is apt to be unstable depending upon the temperature conditions of an outer atmosphere with the result that the electrical characteristics, such as a dielectric strength, dielectric constant, tan 8 etc., of an insulating material used for the conductor or the conductor leading wire are disadvantageously affected to cause a temperature variation.

The object of this invention is to provide a structure of the terminal portion of a cable capable of leading out a conductor up to a normal temperature area in a state stable from the heat insulating and electrical viewpoint with an optimal temperature gradient formed along a conductor leading wire according to the kind of cables.

Another object of this invention is to provide a structure of the terminal portion of a cable capable of preventing the deterioration of an insulating characteristic brought about by the freezing of an insulating oil within a bushing through which a conductor leading wire extends.

' To attain the aforementioned object a conductor portion of the terminal portion of a cable is connected to a conductor leading wire and encased within a terminal box; the conductor leading wire is led out up to a normal temperature area in a manner to extend through a bushing; the portion of the bushing and the terminal box arehoused within a tank; and the circulation of a respective coolant within the terminal box, tank and bushing permits the conductor leading wire to be led out upto a normal temperature area with a temperature gradient formed along the conductor leading wire. As a result, there is obtained a structure of the terminal portion of a cable more stable in heat insulating and electrical insulating characteristics.

To attain another object of this invention, a hollow passageway is provided along the longitudinal direction of the conductor leading wire extending through the bushing, and the circulation of an insulating oil through the bushing prevents freezing of the insulating oil, thus permitting insulating characteristics to be maintained.

The present invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 shows a construction of the terminal portion of a very low temperature cable which is one embodiment of this invention;

F l6. 2 is a view in cross section showing a construction of the terminal portion of a superconductive cable which is another embodiment of this invention; and

FIG. 3 is a cross sectional view 'of the internal structure of another bushing corresponding to the bushing portion as shown in FIGS. 1 and 2.

Referring to FIG. 1 there is shown a construction of the terminal portion of a very low temperature cable adapted to be used at a temperature approximate to about -.-200C.- A cable 1 has a coolant ofliquid nitrogen 5' filled between an insulating layer 3 of a conductor 2. and a pipe 4. The interior of the pipe 4 constitutes a vacuum heat insulating layer 6. The terminal portion of the conductor 2 is reinforced with a reinforcedinsulating layer 7 made of such as an insulating paper, plastic insulating paper, etc., and is connected to a conductor'leading wire 8. The terminal portion of the conductor 2 is encased within a terminal box 9. Within the terminal box 9 is filled liquid nitrogen coolant in communication with the interior of pipe 4a which is within pipe 4. The terminal box 9 has an inlet pipe 10 and an outlet pipe 11 to permit the liquid nitrogen 5 to be circulated in a direction indicated by arrows, thereby maintaining substantially constant the cooling temperature of that portion of the conductor within the terminal box 9. As an inner -pressure resisting, reinforced barrel constituting the terminal box, use is made of F. R. P. (Fiber Reinforced Plastic) capable of coexisting with the liquid nitrogen. The top of the reinforced barrel is blocked by a metal fitting 31. The liquid nitrogen used isof the order of 5 to lOKg/cm at to 100K.

The reinforced insulating layer has the liquid nitrogen impregnated therein.

The conductor leading wire 8 extends through a bushing'l3 and may be led out up to a normal temperature area. Between the terminal box 9 and the bushing 13 another reinforced insulating layer 14 is arranged. Even when the terminal box and the bushing are moved closer to each other, an insulation breakage due to an along-the-surface stress can be prevented. The bushing 13 has an upper inner pressure resisting reinforced barre] 16 and a lower inner pressure resisting, reinforced barrel 17; The top and bottom of the bushing are blocked by metal fittings l8 and 19 respectively. At the connecting portion of the barrels l6 and 17 inlet and outlet pipes 20 and 21 are connected to permit a coolant gaseous nitrogen 22, for example, of the order of 10 Kg/cm at 200K to be circulated in a direction indicated by arrows. The conductor leading wire 8 within the bushing 13 is reinforced at its circumference with an insulating layer 15.

The lower reinforced barrel 17 of the bushing 13, the reinforced insulating layer 14 and the terminal box 9 are all housed within a tank 23. The tank 23 is manufactured from stainless steel, etc, at the outside of which is formed a vacuum heat insulating layer 24. Within the tank 23 a liquid nitrogen coolant 25 of the order of5 to 10 Kg/cm at to K is filled. To the upper and lower sides of the tank 23 inlet and outlet pipes 26 and 27 are connected to allow the coolant to be circulated in a direction indicated by arrows. At the outside of the reinforced barrel an insulator 28 is capped through an interior space in which an insulating oil 29 is filled. The top of the insulator tube is blocked by a metal fitting 30.

With the terminal portion of the cable so constructed Joule heats radiated from the conductor and conductor leading wire and a heat transmitted from a normal temperature area are cooled by the liquid nitrogen 5 circulated within the terminal box 9, the liquid nitrogen 25 3 circulated within the tank 23 and the nitrogen gas circulated within the bushing 13 with the result that the conductor can be led out up to a normal temperature area with a temperature gradient formed along the cond uctor leading wire. In this case, an optimal electrical insulation can be made for eachpart of the cable by selecting the kind of coolants. For example, for the section of the terminal box 9 the reinforced barrel and the nitrogen coolant are used; for the section of the tank 23 the liquid nitrogen 25 and reinforced insulating layer are used; and for the section of the bushing the insulator tube, reinforced barrel 16 and reinforced insulating layer 15 areused.

Let us explain'the structure of the terminal portion ofa superconductive cable used at a temperature approximate to about 273C.

The structure of this superconductive cable is substantially the same as that of the very low temperature .cable as explained in FIG. 1 except that two tanks are provided with a bushing connected therebetween. The explanation of identical parts is therefore omitted. A conductor leading wire 8 is led out up to the normal temperature area through first and second bushings 32 barrels 35 and 36. The top and bottom of the bushing are closed by metal fittings 33 and 34. Within the bushing a liquid helium coolant 39 of the order of 1.5 Kglcm at 4.79K is flowed in a direction indicated by arrows with the bushing filled with the coolant. Around the connecting wire within the bushing 32 a'reinforced insulating layer 40 is provided. The lower reinforced barrel 36 of the bushing and the terminal box 9 are housed within a first tank .41 in which, for example, a liquid helium gas of the order of l.5 Kg/cm 2 at 4.7K is filled as a coolant 70. The coolant can be circulated through the interio'r of the tank from an inlet pipe 42 to an outlet pipe43. At the outside of the first tank 41 a'yacuum heat insulating layer 45 is provided;

A second tank.44 houses an upper inner pressure resisting, reinforced barrel 35 of the first bushing 32 and a. lower inner pressure resisting, reinforced barrel 17. Within the tank aliquid nitrogen 46, for example, of the orderjof to Kg/cm at 95t0 100Kis filled as a coolant. The coolant is circulated through the interior heat insulating layer 49 is provided. With the abovementioned embodiment the conductor of the cable is led out up to a normal temperature area with a temperature gradient formed along the conductor leading wire. As a result, stability is obtained from the heat insulating or electrical insulating standpoint as in the embodiment of FIG. 1. Particularly'the coolants are so placed alongthe conductor leading wire that a liquid nitrogen cooling area is formed between the liquid helium cooling area and the normal temperature area. This minimizes an increase in temperature of the liquid helium, permitting a cooling efficiency to be enhanced. A optimal temperature gradient can be obtained by selecting, according to the kind of cables used, the kind of coolants and the order of their placement, the pres- 4 F 1G. 3 shows the internal structure of a bushing corresponding to the bushing of the embodiments as shown in lGS. land 2 and adapted to prevent an insulating oil within the bushing from freezing. As shown in FIG. 3 a conductor leading wire 8 extending through the bushing 13 is bored along a centeraxis to provide a hollow passageway 50 the top and bottom of which is communicated, through communication passageways 51 and 52, with the interior of an insulator tube 28 in which an insulating oil is filled.

The insulator 28 of the bushing 13 and a lower inner pressure resisting, reinforced barrel 17 are supportingly connected through a metal supporter 53 the interior of which is partitioned by a partition plate 54 to provide upper and lower segments. To the part of the metal supporter 53 pipes 55 and 56 are connected. Through a circulation circuit outside the bushing leading to the pipes 55 and 56 an insulating oil isintroduced into the lower segment of the metal support and passed up through the hollow passageway 50 of the conductor leading wire 8 to the upper segment of the metal support and then to the outside circulation circuit.

The circulation circuit is hydraulically operated by an oil pump 57 and hydraulic tank 58. Provided between the oil pump 57 and hydraulic tank 58 are a heating device 59 for maintaining the temperature of the insulating oil 29 at more than the melting point when cooling is necessary before the electrical conductor of the cable conductor, and a cooling device 60 for cooling the temperature of the insulating oil 29 when the temperature of the conductor leading wire 8 is raised to more than necessary extent at the time of the conduction of the cable conductor. Where the insulating oil is contacted with an air at the normal temperature to attain such an object, then a heating device may be omitted. The circulation circuit may be used in a form that'the cooling device 60 is omitted. When an insulating oil is circulated within the bushing using such circulation circuit, there is no fear that the insulating oil will be frozen, even if liquid nitrogen whose freezing point is about 200C is nearer to the insulating-oil whose freezing point at the lower portion of the bushing is about 60C.lf'the' insulating oil is frozen to v sulator tube with the consequent destruction of the cause a smooth flow of the insulating oil to be disadvan- 'tageously affected, voids will be created in the inner wall of the insulator-tube with the result that a corona discharge occurs at the void in the inner wall of the ininner wall. According to this invention the degeneration of an electrical insulating characteristic is also preyented. Furthermore, a coolant effect can beensaid conductor leading wire leading out from said terminal box; means associated with said bushing for accommodating a flow of gaseous nitrogen through said second chamber; an insulator tube surrounding a portion of said bushing and cooperating therewith to form 'a third chamber adapted to contain insulating oil; a

said structure to a normal temperature area, with a temperature gradient being maintained along the segments of said cable conductor and said conductor leading wire contained within their respective aforesaid chambers.

2. A structure of the terminal portion of a cable according to claim 1 wherein said conductor leading wire extending through the bushing has a hollow passageway along the axial direction thereof; and said bushing is partitioned by a partition plate into chamber segments to permit the insulating oil filled within the two chamber segments to be circulated through the hollow passageway of the conductor leading wire, and pump means for circulating the insulating oil through the two chamber segments of the bushing,

3. A structure of the terminal portion of a cable comprising: a conductor leading wire connected to the terminal of a cable conductor; a terminal box forming a first chamber containing the terminals of said conductor leading wire and said cable conductor; means associated with said terminal box for accommodating a flow of liquid nitrogen through said first chamber; a

first bushing forming a second chamber containing a segment of the conductor leading wire leading out from said terminal box; means associated with said first bushing for accommodating a flow of liquid helium through said second chamber; a first tank forming a third chamber containing a portion of said terminal box and a portion of said first bushing contained therein; means associated with said first tank for accommodating a flow of liquid helium through said third chamber; a second bushing forming a fourth chamber containing a segment of the conductor leading wire leading out from said first bushing; means associated with said second bushing for accommodating a flow of gaseous nitrogen through said fourth chamber; an insulator tube surrounding a portion of said second bushing and cooperating therewith to form a fifth chamber; means associated with said insulating tube for accommodating a flow of insulating oil through said fifth chamber; a second tank forming a sixth chamber containing portions of said first and second bushings therein; and means associated with said second tank for accommodating a flow of liquid nitrogen through said sixth chamber; whereby said conductor leading wire extends out from said structure to a normal temperature area, with a temperature gradient being maintained along the segments of said cable conductor and said conductor leading wire contained within their respective aforesaid chambers.

4. A structure of the terminal portion of a cable according to claim 3 wherein said conductor leading wire extending through said second bushing has a hollow passageway along the axial direction thereof; and said second bushing is partitioned by a partition plate into two segments to permit the insulating oi] filled within the two segments to be circulated through the hollow passageway of the conductor leading wire, and pump means for circulating the insulating oil through the two segments of the bushing. 

1. A structure of the terminal portion of a cable comprising: a conductor leading wire connected to the terminal of a cable conductor; a terminal box forming a first chamber containing the terminals of said conductor leading wire and said cable conductor; means associated with said terminal box for accommodating a flow of liquid nitrogen through said first chamber; a bushing forming a second chamber surrounding a segment of said conductor leading wire leading out from said terminal box; means associated with said bushing for accommodating a flow of gaseous nitrogen through said second chamber; an insulator tube surrounding a portion of said bushing and cooperating therewith to form a third chamber adapted to contain insulating oil; a tank forming a fourth chamber containing the other portion of said bushing and said terminal box; and, means associated with said tank for accommodating a flow of liquid nitrogen through said fourth chamber; whereby said conductor leading wire extends out from said structure to a normal temperature area, with a temperature gradient being maintained along the segments of said cable conductor and said conductor leading wire contained within their respective aforesaid chambers.
 2. A structure of the terminal portion of a cable according to claim 1 whereIn said conductor leading wire extending through the bushing has a hollow passageway along the axial direction thereof; and said bushing is partitioned by a partition plate into chamber segments to permit the insulating oil filled within the two chamber segments to be circulated through the hollow passageway of the conductor leading wire, and pump means for circulating the insulating oil through the two chamber segments of the bushing.
 3. A structure of the terminal portion of a cable comprising: a conductor leading wire connected to the terminal of a cable conductor; a terminal box forming a first chamber containing the terminals of said conductor leading wire and said cable conductor; means associated with said terminal box for accommodating a flow of liquid nitrogen through said first chamber; a first bushing forming a second chamber containing a segment of the conductor leading wire leading out from said terminal box; means associated with said first bushing for accommodating a flow of liquid helium through said second chamber; a first tank forming a third chamber containing a portion of said terminal box and a portion of said first bushing contained therein; means associated with said first tank for accommodating a flow of liquid helium through said third chamber; a second bushing forming a fourth chamber containing a segment of the conductor leading wire leading out from said first bushing; means associated with said second bushing for accommodating a flow of gaseous nitrogen through said fourth chamber; an insulator tube surrounding a portion of said second bushing and cooperating therewith to form a fifth chamber; means associated with said insulating tube for accommodating a flow of insulating oil through said fifth chamber; a second tank forming a sixth chamber containing portions of said first and second bushings therein; and means associated with said second tank for accommodating a flow of liquid nitrogen through said sixth chamber; whereby said conductor leading wire extends out from said structure to a normal temperature area, with a temperature gradient being maintained along the segments of said cable conductor and said conductor leading wire contained within their respective aforesaid chambers.
 4. A structure of the terminal portion of a cable according to claim 3 wherein said conductor leading wire extending through said second bushing has a hollow passageway along the axial direction thereof; and said second bushing is partitioned by a partition plate into two segments to permit the insulating oil filled within the two segments to be circulated through the hollow passageway of the conductor leading wire, and pump means for circulating the insulating oil through the two segments of the bushing. 